Universal Mobile Telecommunications System (UMTS) is one of the third-generation (3G) cell phone technologies. Currently, the most common form of UMTS uses W-CDMA (Wideband Code Division Multiple Access) as the underlying air interface. It is standardized by the 3GPP (3rd Generation Partnership Project), and is the European answer to the ITU IMT-2000 requirements for 3G cellular radio systems.
To differentiate UMTS from competing network technologies, UMTS is sometimes marketed as 3GSM, emphasizing the combination of the 3G nature of the technology and the GSM standard which it was designed to succeed.
In UMTS, for example, rate matching is used to match the amount of data to be transmitted to the available capacity of the different physical channels. It can be done either through puncturing the bits (applicable for both uplink and downlink) if there is too much data for the capacity of the physical channel, or through repeating the bits (applicable for uplink) if there is a fewer number of bits when compared to the physical channel capacity.
DTX (discontinuous transmission) is employed in UTRA TDD systems, (1.28 Mcps and 3.84 Mcps), on a CCTrCH (Coded composite Transport Channel) basis when there is no data to transmit for this CCTrCH. A CCTrCH supports a portion or all of the transmissions of a user. A user may use one or more CCTrCH's within a given timeslot. When DTX is activated for a CCTrCH, there is no transmission on any physical channel supporting this CCTrCH, except for the first physical channel and only every Special Burst Generation Period (SBGP) frames (for uplink(UL)) or every Special Burst Scheduling Parameter (SBSP) frames (for Down Link (DL)), where SBGP or SBSP is configured at radio link setup. The use of DTX results in significant system and user performance benefits as less interference is generated in the system, and handset battery life may be conserved in the UL.
For the DL rate matching, if the number of bits to be transmitted is lower than the maximum allowed bits, then DTX indication bits are used to fill up the radio frame. DTX indication bits only indicate when the transmission should be turned off, they are not transmitted.
Unlike UL, where the data rate can be changed every TTI (Transmission Time Interval), the downlink data rate is fixed, unless changed via higher layer scheduling or through the use of compress mode patterns.
The current consumption during a call is a problem in UMTS. In release 6, for example, it is possible to have a functioning DTX in which a burst is only send a 10th of the slot time; during Transmit Power Control (TPC) information. It means that both DPDCH (Dedicated Physical Data CHannel) and DPCCH (Dedicated Physical Control CHannel) could be quiet and the transmission radio frequency (TX RF) could be shut off during that time. It's called Fractional DCH, which comprises only pilot symbols and TPC commands, with multiple users multiplexed on to the same channel code in such a way that each user uses the channel code for only a fraction of each timeslot.
However, the call will consume a substantial amount of power in UMTS and there is no GPRS similar state available.
UMTS power control comprises open loop power control, inner loop power control, and outer loop power control.
Open loop power control is the ability of the UE transmitter to sets its output power to a specific value. It is used for setting initial uplink and downlink transmission powers when a UE is accessing the network.
Inner loop power control in the uplink is the ability of the UE transmitter to adjust its output power in accordance with one or more TPC commands received in the downlink, in order to keep the received uplink Signal-to-Interference Ratio (SIR) at a given SIR target. The UE transmitter is capable of changing the output power with a step size of 1, 2, and 3 dB, in the slot immediately after the TPC_cmd can be derived. Inner loop power control frequency is 1500 Hz.
The serving cells estimate SIR of the received uplink DPCH, generate TPC commands (TPC_cmd) and transmit the commands once per slot according to the following rule: if SIRest>SIRtarget, then the TPC command to transmit is “0”, while if SIRest<SIRtarget, then the TPC command to transmit is “1”. Upon receipt of one or more TPC commands in a slot, the UE derives a single TPC command for each slot, combining multiple TPC commands if more than one is received in a slot.
Outer loop power control is used to maintain the quality of communication at the level of bearer service quality requirement, while using as low power as possible. The uplink outer loop power control is responsible for setting a target SIR in the Node B for each individual uplink inner loop power control. This target SIR is updated for each UE according to the estimated uplink quality (BLock Error Ration, Bit Error Ratio) for each Radio Resource Control connection. The downlink outer loop power control is the ability of the UE receiver to converge to required link quality (BLER) set by the network (RNC) in downlink.
Power control of the downlink common channels is determined by the network. In general the ratio of the transmit power between different downlink channels is not specified in 3GPP specifications and may change with time, even dynamically.
Additional special situations of power control are power control in compressed mode and Downlink power during handover.